Thin aerogel materials

ABSTRACT

The present invention provides a fiber-reinforced aerogel material which can be used as insulation in thermal battery applications. The fiber-reinforced aerogel material is highly durable, flexible, and has a thermal performance that exceeds the insulation materials currently used in thermal battery applications. The fiber-reinforced aerogel insulation material can be as thin as 1 mm less, and can have a thickness variation as low as 2% or less. Also provided is a method for improving the performance of a thermal battery by incorporating a reinforced aerogel material into the thermal battery. Further provided is a casting method for producing thin fiber-reinforced aerogel materials.

REFERENCE TO PRIOR FILED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/738,193, filed Jun. 12, 2015, which claims the benefit of U.S.Provisional Application 62/015,757 filed Jun. 23, 2014 under 35 U.S.C. §119(e); which applications are incorporated by reference herein in theirentirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under ContractHQ0147-12-C-0012 awarded by the Missile Defense Agency of the Departmentof Defense. The Government has certain rights in this invention.

BACKGROUND

Thermal batteries are batteries that employ inorganic salt electrolytesas barrier agents. Most thermal batteries are composed of a series ofthermal cells, each having an anode, an electrolyte barrier, a cathode,and a pyrotechnic heating mass. The electrolyte barrier functions as aseparator between the anode and the cathode, and is a relativelynon-conductive solid at ambient temperatures. The thermal cells thusremain completely inert while the battery is stored at normaltemperatures and the electrolyte barrier remains solid.

The thermal battery is activated by ignition of the pyrotechnic heatingmass. This pyrotechnic initiation is normally provided by an energyimpulse from a built-in initiator such as an electric match. Theignition of the pyrotechnic heating mass releases sufficient heat intothe cell to melt the solid electrolyte barrier material into anelectro-conductive liquid material. Ion exchange between the cathode andanode through the melted electro-conductive liquid material can thenproduce an electrical current which is transmitted through the terminalsof the battery and into an external load.

A primary challenge in designing thermal batteries is heat management.Once activated, a thermal battery will continue to provide electricalenergy as long as the electrolyte remains molten, or until the activeelectro-generating materials reach the point of functional exhaustion.It is therefore critical to keep the temperature inside the batteryabove the melting point of the electrolyte for as long as possible. Itis also important that the thermal battery be as small as possible toreduce the weight, cost, and design limitations associated with largerbatteries.

An effective approach to improving the life of a thermal battery is byimproving the thermal insulation of the cells. An improvement to theinsulation in a thermal battery will reduce heat loss from the cells,and better preserve the heat being generated by the pyrotechnic heatingmass. It is important that insulation materials within the thermalbattery have a uniform thickness to allow for reliable and predictableperformance of the thermal battery.

Aerogels are among the most effective insulators known to man. Aerogelsare formed by using innovative processing and drying techniques toreplace the interstitial liquid phase of a gel with air. Theseinnovative processing and drying techniques can reduce the capillarypressure and surface tension generated by evaporation in small pores,which often causes significant pore collapse and gel shrinkage during atraditional solvent extraction process.

However, aerogels can also be extremely brittle and difficult to handle.It is particularly difficult to incorporate aerogels into thermalbatteries due to significant design and space limitations associatedwith thermal batteries. A need therefore exists for the development ofreinforced aerogel materials which are uniformly thin, durable, easy tohandle, and which have thermal insulation properties optimized forthermal battery applications.

SUMMARY OF THE INVENTION

The present invention provides a uniformly thin, fiber-reinforcedaerogel insulation material which can be used in thermal batteryapplications. The fiber-reinforced aerogel insulation material is highlydurable, flexible, and has a thermal performance that exceeds theinsulation materials currently used in thermal battery applications. Thefiber-reinforced aerogel insulation material can be as thin as 1 mm orless, and can have a thickness variation as low as 3% or less.

In one embodiment, the present invention provides a reinforced aerogelmaterial having an average thickness of less than 10 mm and a thicknessvariation of less than 15%. Aerogel materials of the present inventioncan have a thickness of less than 10 mm, less than 7.5 mm, less than 5mm, less than 4 mm, less than 3 mm, less than 2 mm, and less than 1 mm.Aerogel materials of the present invention can have a thicknessvariation of less than 15%, less than 10%, less than 8%, less than 6%,less than 5%, less than 4%, less than 3%, and less than 2%. In apreferred embodiment, the present invention provides a fiber-reinforcedaerogel material having an average thickness of less than 2 mm, athickness variation of less than 5%, and a thermal conductivity of about25 mW/mK or less.

In another embodiment, the present invention provides a thermal batterycomprising a reinforced aerogel material. The reinforced aerogelmaterial can have an average thickness of less than 10 mm and athickness variation of less than 15%. In a preferred embodiment, thethermal battery comprises a reinforced aerogel material having anaverage thickness of 2 mm or less, a thickness variation of 5% or less,and a thermal conductivity of about 25 mW/mK or less.

The present invention also provides a method for improving theperformance of a thermal battery by incorporating a reinforced aerogelmaterial into the thermal battery. In one embodiment, the reinforcedaerogel material is incorporated into a thermal battery which previouslylacked an insulation material. In another embodiment, the reinforcedaerogel material is used to replace an existing insulation material in athermal battery. In still another embodiment the reinforced aerogelmaterial is incorporated into a thermal battery which has an existinginsulation material, wherein the reinforced aerogel material provides anadditional layer of insulation in the thermal battery.

The incorporation of the reinforced aerogel material into the thermalbattery can result in an improved battery performance for the thermalbattery, with the increase in performance resulting primarily from theincorporation of the reinforced aerogel material into the thermalbattery. In one embodiment, the improved battery performance for thethermal battery, when measured at about −54° C., can be: i) an improvedbattery performance for 1V run time of up to about 300%; ii) an improvedbattery performance for 16V run time of up to about 250%; or iii) animproved battery performance for 22V run time of up to about 200%. Inanother embodiment, the improved battery performance for the thermalbattery, when measured at about 21° C., can be: i) an improved batteryperformance for 1V run time of up to about 215%; ii) an improved batteryperformance for 16V run time of up to about 200%; or iii) an improvedbattery performance for 22V run time of up to about 175%.

The present invention further provides a method for producing a thinfiber-reinforced aerogel material using a casting system. In oneembodiment, the method can comprise the following steps: a) providing acasting surface and a casting frame, wherein an inner boundary of thecasting frame encloses a casting area on the casting surface; b)producing a sol-gel solution; c) placing a fiber reinforcement materialinto the casting area; d) dispensing the sol-gel solution into thecasting area; e) applying pressure to the sol-gel solution to promotespreading of the sol-gel solution through the fiber reinforcementmaterial in the casting area; f) allowing the sol-gel solution to gel,thereby forming a gel material; and g) drying the gel material toproduce a fiber-reinforced aerogel material. Step (e) can occur eitherbefore or at the same time as step (f).

In another embodiment, the casting method further comprises applyingpressure to the sol-gel solution to promote spreading of the sol-gelsolution through the fiber reinforcement material in the casting areauntil the thickness of the sol-gel solution is the same as the thicknessof the casting frame. Pressure can be applied to the sol-gel solutionwith a pressure source, such as a press or a roll bar. The pressure fromthe pressure source can be continuously applied to the sol-gel solutionuntil the resulting gel has a uniform thickness comparable to the targetthickness of the casting frame. The resulting fiber-reinforced aerogelmaterial can have an average thickness of 5 mm or less, a thicknessvariation of 10% or less, and a thermal conductivity of about 25 mW/mKor less. The resulting fiber-reinforced aerogel material from thecasting method can also be incorporated into a thermal battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 h depict a method for producing thin aerogel materials of auniform thickness, according to one embodiment of the invention.

FIG. 2 illustrates a casting table 100 which can be used for theproduction of thin aerogel materials, according to one embodiment of theinvention.

FIG. 3 shows an aerogel material having a thickness of about 0.07 inches(˜1.75 mm) to about 0.08 inches (˜2 mm), according to one embodiment ofthe invention.

FIG. 4 shows an aerogel material having a thickness of about 0.03 inches(˜0.75 mm) to 0.04 inches (˜1 mm), according to one embodiment of theinvention.

FIG. 5 is a chart depicting the thickness and thickness variation ofmultiple samples of an aerogel material having a target thickness ofabout 0.07 inches (˜1.75 mm) to about 0.08 inches (˜2 mm), according toone embodiment of the invention.

FIG. 6 is a chart depicting the thickness and thickness variation ofmultiple samples of an aerogel material having a target thickness ofabout 0.03 inches (˜0.75 mm) to 0.04 inches (˜1 mm), according to oneembodiment of the invention.

FIG. 7 is a table listing the thermal conductivity of multiple samplesof an aerogel material according to one embodiment of the invention atdifferent calcination states, temperatures, and pressures.

FIG. 8 is a chart depicting the thermal conductivity of multiple samplesof an aerogel material according to one embodiment of the invention atdifferent calcination states, temperatures, and pressures.

FIG. 9 is a chart depicting the voltage output over time at 70° F. (21°C.) of a thermal battery comprising various combinations of insulationmaterials, including an aerogel material according to one embodiment ofthe present invention.

FIG. 10 is a chart depicting the voltage output over time at −65° F.(−54° C.) of a thermal battery comprising various combinations ofinsulation materials, including an aerogel material according to oneembodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides a fiber-reinforced aerogel insulationmaterial which can be used in thermal battery applications. Thefiber-reinforced aerogel material of the present invention is highlydurable, flexible, and has a thermal performance that exceeds theinsulation materials currently used in thermal battery applications. Thefiber-reinforced aerogel material can be as thin as 1 mm or less, andcan have a thickness variation as low as 2% or less. The combination ofuniform thinness and improved insulating capability in the aerogelmaterial of the present invention allows for the production of morecapable thermal batteries with extended operational lifetimes andimproved practical energy densities, while also reducing the insulationcost to the thermal battery system.

The present invention also provides a method for improving theperformance of a thermal battery by incorporating a reinforced aerogelmaterial into the thermal battery. The incorporation of a reinforcedaerogel material into the thermal battery can result in an improvedbattery performance for the thermal battery, with the increase inperformance resulting primarily from the incorporation of the reinforcedaerogel material into the thermal battery. The improved batteryperformance for the improved thermal battery can be up to about 300%improvement over the original thermal battery.

The present invention further includes a method of producing uniformlythin aerogel materials. The method uses a casting table comprising acasting surface, and a casting frame that encloses a casting area on thecasting surface. A fiber-reinforced gal can be cast in the casting areaof the casting table, with the casting frame providing a template foruniform thickness of the gel material being cast. The method can alsoinclude a source of pressure which applies a uniform pressure across themajority or the entirety of the gel material to promote spreading andthinning of the aerogel material through the entire area of the castingarea. The pressure can be applied until the gel material has a uniformthickness comparable to the target thickness of the casting frame.Aerogels are a class of porous materials with open-cells comprising aframework of interconnected structures, with a corresponding network ofpores integrated within the framework, and an interstitial phase withinthe network of pores which is primarily comprised of gases such as air.Aerogels are typically characterized by a low density, a high porosity,a large surface area, and small pore sizes. Aerogels can bedistinguished from other porous materials by their physical andstructural properties, or by the innovative processing and extractiontechniques used to produce them.

Within the context of the present invention, the term “aerogel” or“aerogel material” refers to a gel comprising a framework ofinterconnected structures, with a corresponding network ofinterconnected pores integrated within the framework, and containinggases such as air as a dispersed interstitial medium; and which furthersatisfies at least one of the following characteristics: (1) the gel isat least partially dried using innovative processing and extractiontechniques which cause low pore collapse and low shrinkage to theframework structure of the gel; or (2) the gel is characterized by thefollowing physical and structural properties attributable to aerogels:(a) an average pore diameter ranging from about 2 nm to about 100 nm,(b) a porosity of at least 80% or more, and (c) a surface area of about20 m2/g or more.

Within the context of the present invention, the term “aerogel-likematerial” refers to porous materials which have a gel framework and porestructure similar to aerogels, and which are characterized by thefollowing properties: (a) an average pore diameter ranging from about0.5 nm to about 300 nm; (b) a porosity of at least 50% or more; and (c)a surface area of about 10 m2/g or more.

Aerogel-like materials of the present invention thus include anyaerogels or other open-celled compounds which satisfy the definingelements set forth in previous paragraphs; including compounds which canbe otherwise categorized as xerogels, cryogels, ambigels, microporousmaterials, and the like.

Aerogel materials and aerogel-like materials may also be furthercharacterized by additional physical properties, including: (d) a porevolume of about 2.0 mL/g or more, preferably about 3.0 mL/g or more; (e)a density of about 0.50 g/cc or less, preferably about 0.25 g/cc orless; and (f) at least 50% of the total pore volume comprising poreshaving a pore diameter of between 2 and 50 nm; though satisfaction ofthese additional properties is not required for the characterization ofa compound as an aerogel material or aerogel-like material.

Within the context of the present invention, the term “innovativeprocessing and extraction techniques” refers to methods of replacing aliquid interstitial phase in a wet-gel material with a gas such as air,in a manner which causes low pore collapse and low shrinkage to theframework structure of the gel. Drying techniques, such as ambientpressure evaporation, often introduce strong capillary pressures andother mass transfer limitations at the liquid-vapor interface of theinterstitial phase being evaporated or removed. The strong capillaryforces generated by liquid evaporation or removal can cause significantpore shrinkage and framework collapse within the gel material. The useof innovative processing and extraction techniques during the extractionof a liquid interstitial phase reduces the negative effects of capillaryforces on the pores and the framework of a gel during liquid phaseextraction.

In one embodiment, the innovative processing and extraction techniqueuses near critical or super critical fluids, or near critical or supercritical conditions, to extract the liquid interstitial phase from awet-gel material. This can be accomplished by removing the liquidinterstitial phase from the gel at near or above the critical point ofthe liquid or mixture of liquids. Co-solvents and solvent exchanges canbe used to optimize the near critical or super critical fluid extractionprocess. In another embodiment, the innovative processing and extractiontechnique includes the modification of the gel framework to reduce theirreversible effects of capillary pressures and other mass transferlimitations at the liquid-vapor interface. This embodiment can includethe treatment of a gel framework with a hydrophobizing agent, or otherfunctionalizing agents, which allow a gel framework to withstand orrecover from any collapsing forces during liquid phase extractionconducted below the critical point of the liquid interstitial phase.This embodiment can also include the incorporation of functional groupsor framework elements which provide a framework modulus which issufficiently high to withstand or recover from collapsing forces duringliquid phase extraction conducted below the critical point of the liquidinterstitial phase.

Within the context of the present invention, the terms “framework” or“framework structure” refer to the network of interconnected oligomers,polymers or colloidal particles that form the solid structure of a gelor an aerogel. The polymers or particles that make up the frameworkstructures typically have a diameter of about 100 angstroms. However,framework structures of the present invention can also include networksof interconnected oligomers, polymers or colloidal particles of alldiameter sizes that form the solid structure within in a gel or aerogel.Furthermore, the terms “silica-based aerogel” or “silica-basedframework” refer to an aerogel framework in which silica comprises atleast 50% (by weight) of the oligomers, polymers or colloidal particlesthat form the solid framework structure within in the gel or aerogel.

Within the context of the present invention, the term “aerogelcomposition” refers to any composite material which includes aerogelmaterial as a component of the composite. Examples of aerogelcompositions include, but are not limited to: fiber-reinforced aerogelcomposites; aerogel composites which include additive elements such asopacifiers; aerogel-foam composites; aerogel-polymer composites; andcomposite materials which incorporate aerogel particulates, particles,granules, beads, or powders into a solid or semi-solid material, such asbinders, resins, cements, foams, polymers, or similar solid materials.Within the context of the present invention, the term “aerogel-likecomposition” refers to any composite material which includesaerogel-like materials as an element of the composite.

Within the context of the present invention, the term “reinforcedaerogel composition” refers to aerogel compositions which comprise areinforcing phase within the aerogel material which is not part of theaerogel framework. The reinforcing phase can be any material whichprovides increased flexibility, resilience, conformability or structuralstability to the aerogel material. Examples of well-known reinforcingmaterials include, but are not limited to: open-cell foam reinforcementmaterials, polymeric reinforcement materials, and fiber reinforcementmaterials such as discrete fibers, woven materials, non-woven materials,battings, webs, mats, and felts. Additionally, fiber basedreinforcements may be combined with one or more of the other reinforcingmaterials, and can be oriented continuously throughout or in limitedpreferred parts of the composition.

Within the context of the present invention, the term “fiber-reinforcedaerogel composition” refers to a reinforced aerogel composition whichcomprises a fiber reinforcement material as a reinforcing phase. Fiberreinforcement materials can include, but are not limited to, discretefibers, woven materials, non-woven materials, battings, webs, mats,felts, or combinations thereof. Fiber reinforcement materials cancomprise a range of materials, including, but not limited to:Polyesters, polyolefin terephthalates, poly(ethylene) naphthalate,polycarbonates (examples Rayon, Nylon), cotton, (e.g. lycra manufacturedby DuPont), carbon (e.g. graphite), polyacrylonitriles (PAN), oxidizedPAN, uncarbonized heat treated PANs (such as those manufactured by SGLcarbon), fiberglass based material (like S-glass, 901 glass, 902 glass,475 glass, E-glass) silica based fibers like quartz, (e.g. Quartzelmanufactured by Saint-Gobain), Q-felt (manufactured by Johns Manville),Saffil (manufactured by Saffil), Durablanket (manufactured by Unifrax)and other silica fibers, Duraback (manufactured by Carborundum),Polyaramid fibers like Kevlar, Nomex, Sontera (all manufactured byDuPont), Conex (manufactured by Taijin), poly olefins like Tyvek(manufactured by DuPont), Dyneema (manufactured by DSM), Spectra(manufactured by Honeywell), other polypropylene fibers like Typar,Xavan (both manufactured by DuPont), fluoropolymers like PTFE with tradenames as Teflon (manufactured by DuPont), Goretex (manufactured by W.L.GORE), Silicon carbide fibers like Nicalon (manufactured by COICeramics), ceramic fibers like Nextel (manufactured by 3M), Acrylicpolymers, fibers of wool, silk, hemp, leather, suede, PBO—Zylon fibers(manufactured by Tyobo), Liquid crystal material like Vectan(manufactured by Hoechst), Cambrelle fiber (manufactured by DuPont),Polyurethanes, polyamaides, Wood fibers, Boron, Aluminum, Iron,Stainless Steel fibers and other thermoplastics like PEEK, PES, PEI,PEK, PPS.

Within the context of the present invention, the terms “aerogel blanket”or “aerogel blanket composition” refer to aerogel compositionsreinforced with a continuous sheet of fiber reinforcement material.Aerogel blanket compositions can be differentiated from other fiberreinforced aerogel composition which are reinforced with anon-continuous fiber network, such as separated agglomerates or clumpsof fiber materials. Aerogel blanket compositions are particularly usefulfor applications requiring flexibility, since they are highlyconformable and can be used like a blanket to cover surfaces of simpleor complex geometry, while also retaining the excellent thermalinsulation properties of aerogels. Aerogel blanket compositions andsimilar fiber-reinforced aerogel compositions are described in PublishedUS patent application 2002/0094426 (paragraphs 12-16, 25-27, 38-58,60-88), which is hereby incorporated by reference according to theindividually cited sections and paragraphs.

Within the context of the present invention, the term “wet gel” refersto a gel in which the mobile interstitial phase within the network ofinterconnected pores is primarily comprised of a liquid phase such as aconventional solvent, liquefied gases such as liquid carbon dioxide, ora combination thereof. Aerogels typically require the initial productionof a wet gel, followed by innovative processing and extraction toreplace the mobile interstitial liquid phase in the gel with air.Examples of wet gels include, but are not limited to: alcogels,hydrogels, ketogels, carbonogels, and any other wet gels known to thosein the art.

Within the context of the present invention, the terms “additive” or“additive element” refer to materials which can be added to an aerogelcomposition before, during, or after the production of the aerogel.Additives can be added to alter or improve desirable properties in anaerogel, or to counteract undesirable properties in an aerogel.Additives are typically added to an aerogel material either prior orduring gelation. Examples of additives include, but are not limited to:microfibers, fillers, reinforcing agents, stabilizers, thickeners,elastic compounds, opacifiers, coloring or pigmentation compounds,radiation absorbing compounds, radiation reflecting compounds, corrosioninhibitors, thermally conductive components, phase change materials, pHadjustors, redox adjustors, HCN mitigators, off-gas mitigators,electrically conductive compounds, electrically dielectric compounds,magnetic compounds, radar blocking components, hardeners, anti-shrinkingagents, and other aerogel additives known to those in the art. Otherexamples of additives include smoke suppressants and fire suppressants.Published US Pat. App. 20070272902 A1 (Paragraphs [0008] and[0010]-[0039]) includes teachings of smoke suppressants and firesuppressants, and is hereby incorporated by reference according to theindividually cited paragraphs.

Within the context of the present invention, the terms “flexible” and“flexibility” refer to the ability of an aerogel material or compositionto be bent or flexed without macrostructural failure. Preferably,aerogel materials or compositions of the present invention are capableof bending at least 5°, at least 25°, at least 45°, at least 65°, or atleast 85° without macroscopic failure; and/or have a bending radius ofless than 4 feet, less than 2 feet, less than 1 foot, less than 6inches, less than 3 inches, less than 2 inches, less than 1 inch, orless than ½ inch without macroscopic failure. Likewise, the terms“highly flexible” or “high flexibility” refer to aerogel materials orcompositions capable of bending to at least 90° and/or have a bendingradius of less than ½ inch without macroscopic failure. Furthermore, theterms “classified flexible” and “classified as flexible” refer toaerogel materials or compositions which can be classified as flexibleaccording to ASTM classification standard C1101 (ASTM International,West Conshohocken, Pa.). Aerogel materials or compositions of thepresent invention can be flexible, highly flexible, and/or classifiedflexible. Aerogel materials or compositions of the present invention canalso be drapable. Within the context of the present invention, the terms“drapable” and “drapability” refer to the ability of an aerogel materialor composition to be bent or flexed to 90° or more with a radius ofcurvature of about 4 inches or less, without macroscopic failure. Anaerogel material or composition of the present invention is preferablyflexible such that the composition is non-rigid and may be applied andconformed to three-dimensional surfaces or objects, or pre-formed into avariety of shapes and configurations to simplify installation orapplication.

Within the context of the present invention, the terms “resilient” and“resilience” refer to the ability of an aerogel material or compositionto at least partially return to an original form or dimension followingdeformation through compression, flexing, or bending. Resilience may becomplete or partial, and it may be expressed in terms of percentagereturn. An aerogel material or composition of the present inventionpreferably has a resilience of more than 25%, more than 50%, more than60%, more than 70%, more than 75%, more than 80%, more than 85%, morethan 90%, or more than 95% return to an original form or dimensionfollowing a deformation. Likewise, the terms “classified resilient” and“classified as resilient” refer to aerogel materials or compositionswhich can be classified as resilient flexible according to ASTMclassification standard C1101(ASTM International, West Conshohocken,Pa.).

Within the context of the present invention, the term “self-supporting”refers to the ability of an aerogel material or composition to beflexible and/or resilient based primarily on the physical properties ofthe aerogel and any reinforcing phase in the aerogel composition.Self-supporting aerogel materials or compositions can be differentiatedfrom other aerogel materials, such as coatings, which rely on anunderlying substrate to provide flexibility and/or resilience to thematerial.

Within the context of the present invention, the term “shrinkage” refersto the ratio of: 1) the difference between the measured final density ofthe dried aerogel material or composition, or aerogel-like material orcomposition, and the target density calculated from solid content in thesol-gel precursor solution, relative to 2) the target density calculatedfrom solid content in the sol-gel precursor solution. Shrinkage can becalculated by the following equation: Shrinkage=[Final Density(g/cm3)−Target Density (g/cm3)]/[Target Density (g/cm3)]. Preferably,shrinkage of an aerogel material of the present invention is preferably50% or less, 25% or less, 10% or less, 8% or less, 6% or less, 5% orless, 4% or less, 3% or less, 2% or less, 1% or less, 0.1% or less,about 0.01% or less, or in a range between any two of these values.

Within the context of the present invention, the terms “thermalconductivity” and “TC” refer to a measurement of the ability of amaterial or composition to transfer heat between two surfaces on eitherside of the material or composition, with a temperature differencebetween the two surfaces. Thermal conductivity is specifically measuredas the heat energy transferred per unit time and per unit surface area,divided by the temperature difference. It is typically recorded in SIunits as mW/m*K (milliwatts per meter*Kelvin). The thermal conductivityof a material may be determined by methods known in the art, including,but not limited to: Test Method for Steady-State Thermal TransmissionProperties by Means of the Heat Flow Meter Apparatus (ASTM C518, ASTMInternational, West Conshohocken, Pa.); a Test Method for Steady-StateHeat Flux Measurements and Thermal Transmission Properties by Means ofthe Guarded-Hot-Plate Apparatus (ASTM C177, ASTM International, WestConshohocken, Pa.); a Test Method for Steady-State Heat TransferProperties of Pipe Insulation (ASTM C335, ASTM International, WestConshohocken, Pa.); a Thin Heater Thermal Conductivity Test (ASTM C1114,ASTM International, West Conshohocken, Pa.); Determination of thermalresistance by means of guarded hot plate and heat flow meter methods (EN12667, British Standards Institution, United Kingdom); or Determinationof steady-state thermal resistance and related properties—Guarded hotplate apparatus (ISO 8203, International Organization forStandardization, Switzerland). Within the context of the presentinvention, thermal conductivity measurements are acquired according toASTM C177 or ASTM C518 standards, at a temperature of about 37.5° C. anda compression of about 2 psi, unless otherwise stated. Alternatively,thermal conductivity may also be determined using EN 12667 or otherrelevant standards, when measurements are expressly identified as such.Preferably, aerogel materials or compositions of the present inventionhave a thermal conductivity of about 50 mW/mK or less, about 40 mW/mK orless, about 30 mW/mK or less, about 25 mW/mK or less, about 20 mW/mK orless, about 18 mW/mK or less, about 16 mW/mK or less, about 14 mW/mK orless, about 12 mW/mK or less, about 10 mW/mK or less, about 5 mW/mK orless, or in a range between any two of these values.

Within the context of the present invention, the term “density” refersto a measurement of the mass per unit volume of an aerogel material orcomposition. The term “density” generally refers to the true density ofan aerogel material, as well as the bulk density of an aerogelcomposition. Density is typically recorded as kg/m3 or g/cc. The densityof an aerogel material or composition may be determined by methods knownin the art, including, but not limited to: Standard Test Method forDimensions and Density of Preformed Block and Board-Type ThermalInsulation (ASTM C303, ASTM International, West Conshohocken, Pa.);Standard Test Methods for Thickness and Density of Blanket or BattThermal Insulations (ASTM C167, ASTM International, West Conshohocken,Pa.); or Determination of the apparent density of preformed pipeinsulation (ISO 18098, International Organization for Standardization,Switzerland). Within the context of the present invention, densitymeasurements are acquired according to ASTM C167 standards, unlessotherwise stated. Preferably, aerogel materials or compositions of thepresent invention have a density of about 0.60 g/cc or less, about 0.50g/cc or less, about 0.40 g/cc or less, about 0.30 g/cc or less, about0.25 g/cc or less, about 0.20 g/cc or less, about 0.18 g/cc or less,about 0.16 g/cc or less, about 0.14 g/cc or less, about 0.12 g/cc orless, about 0.10 g/cc or less, about 0.05 g/cc or less, about 0.01 g/ccor less, or in a range between any two of these values.

Within the context of the present invention, the term “liquid waterabsorption” refers to a measurement of the potential of an aerogelmaterial or composition to absorb liquid water. Liquid water absorptioncan be expressed as a percent (by weight) of water which is absorbed orotherwise retained by an aerogel material or composition when exposed toliquid water under certain measurement conditions. The liquid waterabsorption of an aerogel material or composition may be determined bymethods known in the art, including, but not limited to: Standard TestMethod for Determining the Water Retention (Repellency) Characteristicsof Fibrous Glass Insulation (ASTM C1511, ASTM International, WestConshohocken, Pa.); Thermal insulating products for buildingapplications: Determination of short term water absorption by partialimmersion (EN 1609, British Standards Institution, United Kingdom).Within the context of the present invention, measurements of liquidwater absorption are acquired according to ASTM C1511 standards, underambient pressure and temperature, unless otherwise stated. Preferably,aerogel materials or compositions of the present invention can have aliquid water absorption of about 50% or less, about 40% or less, about30% or less, about 20% or less, about 15% or less, about 10% or less,about 8% or less, about 3% or less, about 2% or less, about 1% or less,about 0.1% or less, or in a range between any two of these values. Anaerogel material or composition which has “improved liquid waterabsorption” relative to another aerogel material or composition willhave a lower percentage of liquid water absorption/retention relative tothe reference aerogel materials or compositions.

Within the context of the present invention, the term “water vaporabsorption” refers to a measurement of the potential of an aerogelmaterial or composition to absorb water vapor. Water vapor absorptioncan be expressed as a percent (by weight) of water which is absorbed orotherwise retained by an aerogel material or composition when exposed towater vapor under certain measurement conditions. The water vaporabsorption of an aerogel material or composition may be determined bymethods known in the art, including, but not limited to: Standard TestMethod for Determining the Water Vapor Sorption of Unfaced Mineral FiberInsulation (ASTM C1104, ASTM International, West Conshohocken, Pa.).Within the context of the present invention, measurements of water vaporabsorption are acquired according to ASTM C1104 standards, under ambientpressure and temperature, unless otherwise stated. Preferably, aerogelmaterials or compositions of the present invention can have a watervapor absorption of about 50% or less, about 40% or less, about 30% orless, about 20% or less, about 15% or less, about 10% or less, about 8%or less, about 3% or less, about 2% or less, about 1% or less, about0.1% or less, or in a range between any two of these values. An aerogelmaterial or composition which has “improved water vapor absorption”relative to another aerogel material or composition will have a lowerpercentage of water vapor absorption/retention relative to the referenceaerogel materials or compositions.

Within the context of the present invention, the term “hydrophobicity”refers to a measurement of the ability of an aerogel material orcomposition to repel water. The hydrophobicity of an aerogel material orcomposition can relate to the ability of the material or composition torepel the absorption of liquid water (corresponding to liquid waterabsorption), the ability of the material or composition to repel theabsorption of water vapor (corresponding to water vapor absorption), ora combination thereof. Hydrophobicity of a material or composition canbe expressed as a percent (by weight) of water which is absorbed orotherwise retained by an aerogel material or composition when exposed toliquid water under certain measurement conditions, or when exposed towater vapor under certain measurement conditions. As an example, ahydrophobicity of 50% or less would indicate that an aerogel material orcomposition has either a liquid water absorption of 50% or less, a watervapor absorption of 50% or less, or both. Preferably, aerogel materialsor compositions of the present invention can have a hydrophobicity ofabout 50% or less, about 40% or less, about 30% or less, about 20% orless, about 15% or less, about 10% or less, about 8% or less, about 3%or less, about 2% or less, about 1% or less, about 0.1% or less, or in arange between any two of these values. An aerogel material orcomposition which has “improved hydrophobicity” relative to anotheraerogel material or composition will have improved liquid waterabsorption relative to the reference aerogel materials or compositions,improved water vapor absorption relative to the reference aerogelmaterials or compositions, or both.

Hydrophobicty of an aerogel material or composition can also beexpressed by measuring the equilibrium contact angle of a water dropletat the interface with the surface of the material. Aerogel materials orcompositions of the present invention can have a water contact angle ofabout 90° or more, about 120° or more, about 130° or more, about 140° ormore, about 150° or more, about 160° or more, about 170° or more, about175° or more, or in a range between any two of these values. Within thecontext of the present invention, the terms “super hydrophobic” or“super hydrophobicity” refer materials or compositions which have awater contact angle of about 150° or more.

Within the context of the present invention, the term “thermal battery”refers to a combination of one or more thermal cells. The term “thermalcell” refers to an energy cell that is activated by applying heat tomelt a solidified electrolyte barrier.

Aerogels are described as a framework of interconnected structures whichare most commonly comprised of interconnected oligomers, polymers orcolloidal particles. An aerogel framework can be made from a range ofprecursor materials, including: inorganic precursor materials (such asprecursors used in producing silica-based aerogels); organic precursormaterials (such precursors used in producing carbon-based aerogels);hybrid inorganic/organic precursor materials; and combinations thereof.Within the context of the present invention, the term “amalgam aerogel”refers to an aerogel produced from a combination of two or moredifferent gel precursors.

Inorganic aerogels are generally formed from metal oxide or metalalkoxide materials. The metal oxide or metal alkoxide materials can bebased on oxides or alkoxides of any metal that can form oxides. Suchmetals include, but are not limited to: silicon, aluminum, titanium,zirconium, hafnium, yttrium, vanadium, cerium, and the like. Inorganicsilica aerogels are traditionally made via the hydrolysis andcondensation of silica-based alkoxides (such as tetraethoxylsilane), orvia gelation of silicic acid or water glass. Other relevant inorganicprecursor materials for silica based aerogel synthesis include, but arenot limited to: metal silicates such as sodium silicate or potassiumsilicate, alkoxysilanes, partially hydrolyzed alkoxysilanes,tetraethoxylsilane (TEOS), partially hydrolyzed TEOS, condensed polymersof TEOS, tetramethoxylsilane (TMOS), partially hydrolyzed TMOS,condensed polymers of TMOS, tetra-n-propoxysilane, partially hydrolyzedand/or condensed polymers of tetra-n-propoxysilane, polyethyl silicates,partially hydrolyzed polyethysilicates, monomeric alkylalkoxy silanes,bis-trialkoxy alkyl or aryl silanes, polyhedral silsesquioxanes, orcombinations thereof.

In one embodiment of the present invention, pre-hydrolyzed TEOS, such asSilbond H-5 (SBH5, Silbond Corp), which is hydrolyzed with awater/silica ratio of about 1.9-2, may be used as commercially availableor may be further hydrolyzed prior to incorporation into the gellingprocess. Partially hydrolyzed TEOS or TMOS, such as polyethysilicate(Silbond 40) or polymethylsilicate may also be used as commerciallyavailable or may be further hydrolyzed prior to incorporation into thegelling process.

Inorganic aerogels can also include gel precursors which comprise atleast one hydrophobic group, such as alkyl metal alkoxides, cycloalkylmetal alkoxides, and aryl metal alkoxides, which can impart or improvecertain properties in the gel such as stability and hydrophobicity.Inorganic silica aerogels can specifically include hydrophobicprecursors such as alkylsilanes or arylsilanes. Hydrophobic gelprecursors can be used as primary precursor materials to form theframework of a gel material. However, hydrophobic gel precursors aremore commonly used as co-precursors in combination with simple metalalkoxides in the formation of amalgam aerogels. Hydrophobic inorganicprecursor materials for silica based aerogel synthesis include, but arenot limited to: trimethyl methoxysilane [TMS], dimethyl dimethoxysilane[DMS], methyl trimethoxysilane [MTMS], trimethyl ethoxysilane, dimethyldiethoxysilane [DMDS], methyl triethoxysilane [MTES], ethyltriethoxysilane [ETES], diethyl diethoxysilane, ethyl triethoxysilane,propyl trimethoxysilane, propyl triethoxysilane, phenyltrimethoxysilane, phenyl triethoxysilane [PhTES], hexamethyldisilazaneand hexaethyldisilazane, and the like.

Aerogels may also be treated to impart or improve hydrophobicity.Hydrophobic treatment can be applied to a sol-gel solution, a wet-gelprior to liquid phase extraction, or to an aerogel subsequent to liquidphase extraction. Hydrophobic treatment is especially common in theproduction of metal oxide aerogels, such as silica aerogels. An exampleof a hydrophobic treatment of a gel is discussed below in greaterdetail, specifically in the context of treating a silica wet-gel.However, the specific examples and illustrations provided herein are notintended to limit the scope of the present invention to any specifictype of hydrophobic treatment procedure or aerogel substrate. Thepresent invention can include any gel or aerogel known to those in theart, as well as associated methods of hydrophobic treatment of theaerogels, in either wet-gel form or dried aerogel form.

Hydrophobic treatment is carried out by reacting a hydroxy moiety on agel, such as a silanol group (Si—OH) present on a framework of a silicagel, with a functional group of a hydrophobizing agent. The resultingreaction converts the silanol group and the hydrophobizing agent into ahydrophobic group on the framework of the silica gel. The hydrophobizingagent compound can react with hydroxyl groups on the gel according thefollowing reaction: R_(N)MX_(4-N) (hydrophobizing agent)+MOH(silanol)→MOMR_(N) (hydrophobic group)+HX. Hydrophobic treatment cantake place both on the outer macro-surface of a silica gel, as well ason the inner-pore surfaces within the porous network of a gel.

A gel can be immersed in a mixture of a hydrophobizing agent and anoptional hydrophobic-treatment solvent in which the hydrophobizing agentis soluble, and which is also miscible with the gel solvent in thewet-gel. A wide range of hydrophobic-treatment solvents can be used,including solvents such as methanol, ethanol, isopropanol, xylene,toluene, benzene, dimethylformamide, and hexane. Hydrophobizing agentsin liquid or gaseous form may also be directly contacted with the gel toimpart hydrophobicity.

The hydrophobic treatment process can include mixing or agitation tohelp the hydrophobizing agent to permeate the wet-gel. The hydrophobictreatment process can also include varying other conditions such astemperature and pH to further enhance and optimize the treatmentreactions. After the reaction is completed, the wet-gel is washed toremove unreacted compounds and reaction by-products.

Hydrophobizing agents for hydrophobic treatment of an aerogel aregenerally compounds of the formula: R_(N)MX_(4-N); where M is the metal;R is a hydrophobic group such as CH₃, CH₂CH₃, C₆H₆, or similarhydrophobic alkyl, cycloalkyl, or aryl moieties; and X is a halogen,usually Cl. Specific examples of hydrophobizing agents include, but arenot limited to: trimethylchlorosilane [TMCS], triethylchlorosilane[TECS], triphenylchlorosilane [TPCS], dimethylchlorosilane [DMCS],dimethyldichlorosilane [DMDCS], and the like. Hydrophobizing agents canalso be of the formula: Y(R?M)2; where M is a metal; Y is bridging groupsuch as NH or O; and R is a hydrophobic group such as CH3, CH2CH3, C6H6,or similar hydrophobic alkyl, cycloalkyl, or aryl moieites. Specificexamples of such hydrophobizing agents include, but are not limited to:hexamethyldisilazane [HMDZ] and hexamethyldisiloxane [HMDSO].Hydrophobizing agents can further include compounds of the formula:R_(N)MV_(4-N), wherein V is a reactive or leaving group other than ahalogen. Specific examples of such hydrophobizing agents include, butare not limited to: vinyltriethoxysilane and vinyltrimethoxysilane.

Organic aerogels are generally formed from carbon-based polymericprecursors. Such polymeric materials include, but are not limited to:resorcinol formaldehydes (RF), polyimide, polyacrylate, polymethylmethacrylate, acrylate oligomers, polyoxyalkylene, polyurethane,polyphenol, polybutadiane, trialkoxysilyl-terminatedpolydimethylsiloxane, polystyrene, polyacrylonitrile, polyfurfural,melamine-formaldehyde, cresol formaldehyde, phenol-furfural, polyether,polyol, polyisocyanate, polyhydroxybenze, polyvinyl alcohol dialdehyde,polycyanurates, polyacrylamides, various epoxies, agar, agarose,chitosan, and combinations thereof. As one example, organic RF aerogelsare typically made from the sol-gel polymerization of resorcinol ormelamine with formaldehyde under alkaline conditions.

Organic/inorganic hybrid aerogels are mainly comprised of ormosil(organically modified silica) aerogels. These ormosil materials includeorganic components which are covalently bonded to a silica network.Ormosils are typically formed through the hydrolysis and condensation oforganically modified silanes, R—Si(OX)₃, with traditional alkoxideprecursors, Y(OX)₄. In these formulas: X may represent, for example,CH₃, C₂H₅, C₃H₇, C₄H₉; Y may represent, for example, Si, Ti, Zr, or Al;and R may be any organic fragment such as methyl, ethyl, propyl, butyl,isopropyl, methacrylate, acrylate, vinyl, epoxide, and the like. Theorganic components in ormosil aerogel may also be dispersed throughoutor chemically bonded to the silica network.

Within the context of the present invention, the term “ormosil”encompasses the foregoing materials as well as other organicallymodified ceramics, sometimes referred to as “ormocers.” Ormosils areoften used as coatings where an ormosil film is cast over a substratematerial through, for example, the sol-gel process. Examples of otherorganic-inorganic hybrid aerogels of the invention include, but are notlimited to, silica-polyether, silica-PMMA, silica-chitosan, carbides,nitrides, and other combinations of the aforementioned organic andinorganic aerogel forming compounds. Published US Pat. App. 20050192367(Paragraphs [0022]-[0038] and [0044]-[0058]) includes teachings of suchhybrid organic-inorganic materials, and is hereby incorporated byreference according to the individually cited sections and paragraphs.

Aerogels of the present invention are preferably inorganic silicaaerogels formed primarily from alcohol solutions of hydrolyzed silicateesters formed from silicon alkoxides. However, the invention as a wholemay be practiced with any other aerogel compositions known to those inthe art, and is not limited to any one precursor material or amalgammixture of precursor materials.

Production of an aerogel generally includes the following steps: i)formation of a sol-gel solution; ii) formation of a gel from the sol-gelsolution; and iii) extracting the solvent from the gel materials throughinnovative processing and extraction, to obtain a dried aerogelmaterial. This process is discussed below in greater detail,specifically in the context of forming inorganic aerogels such as silicaaerogels. However, the specific examples and illustrations providedherein are not intended to limit the present invention to any specifictype of aerogel and/or method of preparation. The present invention caninclude any aerogel formed by any associated method of preparation knownto those in the art.

The first step in forming an inorganic aerogel is generally theformation of a sol-gel solution through hydrolysis and condensation ofmetal alkoxide precursors in an alcohol-based solvent. Major variablesin the formation of inorganic aerogels include the type of alkoxideprecursors included in the sol-gel solution, the nature of the solvent,the processing temperature and pH of the sol-gel solution (which may bealtered by addition of an acid or a base), and precursor/solvent/waterratio within the sol-gel solution. Control of these variables in forminga sol-gel solution can permit control of the growth and aggregation ofthe gel framework during the subsequent transition of the gel materialfrom the “sol” state to the “gel” state. While properties of theresulting aerogels are strongly affected by the pH of the precursorsolution and the molar ratio of the reactants, any pH and any molarratios that permit the formation of gels may be used in the presentinvention.

A sol-gel solution is formed by combining at least one gelling precursorwith a solvent. Suitable solvents for use in forming a sol-gel solutioninclude lower alcohols with 1 to 6 carbon atoms, preferably 2 to 4,although other solvents can be used as known to those with skill in theart. Examples of useful solvents include, but are not limited to:methanol, ethanol, isopropanol, ethyl acetate, ethyl acetoacetate,acetone, dichloromethane, tetrahydrofuran, and the like. Multiplesolvents can also be combined to achieve a desired level of dispersionor to optimize properties of the gel material. Selection of optimalsolvents for the sol-gel and gel formation steps thus depends on thespecific precursors, fillers and additives being incorporated into thesol-gel solution; as well as the target processing conditions forgelling and liquid phase extraction, and the desired properties of thefinal aerogel materials.

Water can also be present in the precursor-solvent solution. The wateracts to hydrolyze the metal alkoxide precursors into metal hydroxideprecursors. The hydrolysis reaction can be (using TEOS in ethanolsolvent as an example): Si(OC₂H₅)₄+4H₂O→Si(OH)4+4(C2H5OH). The resultinghydrolyzed metal hydroxide precursors remain suspended in the solventsolution in a “sol” state, either as individual molecules or as smallpolymerized (or oligomarized) colloidal clusters of molecules. Forexample, polymerization/condensation of the Si(OH)₄ precursors can occuras follows: 2 Si(OH)₄═(OH)₃Si—O—Si(OH)₃+H₂O. This polymerization cancontinue until colloidal clusters of polymerized (or oligomarized) SiO₂(silica) molecules are formed.

Acids and bases can be incorporated into the sol-gel solution to controlthe pH of the solution, and to catalyze the hydrolysis and condensationreactions of the precursor materials. While any acid may be used tocatalyze precursor reactions and to obtain a lower pH solution,preferable acids include: HCl, H₂SO₄, H₃PO₄, oxalic acid and aceticacid. Any base may likewise be used to catalyze precursor reactions andto obtain a higher pH solution, with a preferable base comprising NH₄OH.

The sol-gel solution can include additional co-gelling precursors, aswell as filler materials and other additives. Filler materials and otheradditives may be dispensed in the sol-gel solution at any point beforeor during the formation of a gel. Filler materials and other additivesmay also be incorporated into the gel material after gelation throughvarious techniques known to those in the art. Preferably, the sol-gelsolution comprising the gelling precursors, solvents, catalysts, water,filler materials and other additives is a homogenous solution which iscapable of effective gel formation under suitable conditions.

Once a sol-gel solution has been formed and optimized, the gel-formingcomponents in the sol-gel can be transitioned into a gel material. Theprocess of transitioning gel-forming components into a gel materialcomprises an initial gel formation step wherein the gel solidifies up tothe gel point of the gel material. The gel point of a gel material maybe viewed as the point where the gelling solution exhibits resistance toflow and/or forms a substantially continuous polymeric frameworkthroughout its volume. A range of gel-forming techniques are known tothose in the art. Examples include, but are not limited to: maintainingthe mixture in a quiescent state for a sufficient period of time;adjusting the pH of the solution; adjusting the temperature of thesolution; directing a form of energy onto the mixture (ultraviolet,visible, infrared, microwave, ultrasound, particle radiation,electromagnetic); or a combination thereof.

A mold may be used to cast the gel materials of the present inventioninto desired shapes. One benefit of using a mold may be an improvedaesthetic appearance. Another benefit may be the creation of features inthe gel material which are difficult or damaging to produce without moldcasting. Such features include, but are not limited to: holes,depressions, protrusions and patterns; all of which can allow for abetter fit between the final aerogel material and a supportingstructure. Reinforced aerogel materials can also be incorporated intothis molding procedure.

A casting table may be also used to cast the gel materials of thepresent invention. FIG. 2 illustrates a casting table 100 which can beused for the production of aerogel insulation sheets. The casting table100 comprises an underlying casting surface 110 which can be coveredwith a non-stick coating or material, such as Teflon. The casting table100 can also comprises an overlying casting frame 112 which has an outerperimeter 106 and an inner perimeter 104. The inner perimeter 104 ofcasting frame 112 encloses a casting area 102 on the casting surface110. The thickness of the casting frame 112 can be adjusted to match atarget thickness for the gel material being cast. The thickness of thecasting frame 112 can then be used as a thickness template to ensurethat the thickness of the resulting gel material matches the initialtarget thickness of the gel material.

FIGS. 1 a-1 h depict a preferred embodiment of the casting table whichcomprises a 4 ft×6 ft casting table coated with a Teflon sheet. A 4 ft×6ft sheet of PETG (polyethylene terephthalate glycol-modified) having athickness of 0.078 inches (˜2 mm) was placed onto the casting table. A 3ft×5 ft rectangle of PETG material was cut and removed from the interiorof the 4 ft×6 ft PETG sheet. The remaining PETG material providedthickness control during the subsequent casting of the aerogel material.The thickness of the PETG material was chosen to provide a final castthickness of between about 0.07 inches (˜1.75 mm) and about 0.08 inches(˜2 mm) for the aerogel insulation material.

To ensure that the gel material being cast on the casting table has auniform thickness which matches the target thickness of the castingframe, a source of pressure can be applied to the gel material duringthe casting process, or subsequent to the casting process but prior tocomplete gelation of the gel material. The source of pressure can be anydevice which can be used to apply uniform pressure across the majorityor the entirety of the gel material.

In one embodiment, the source of pressure comprises a solid sheet suchas a press which extends over the entirety of the casting area 102. Thesolid sheet is used to apply a downward force onto the gel material inthe cast to promote spreading and thinning of the aerogel materialthrough the entire area of the casting area 102. A downward forcecontinues to be applied until the solid sheet contacts the casting frameon all sides, thus providing a gel material of a uniform thicknesscomparable to the target thickness of the casting frame 112.

In another embodiment, the source of pressure comprises a roller bar 108which extends across a span of the casting area 102. The roller bar 108is used to apply a downward force onto the gel material in the cast topromote spreading and thinning of the aerogel material through theentire area of the casting area 102. The roller bar 108 can be advancedalong the span of the casting area 102, and a downward force is appliedto the roller bar 108 to maintain contact between the roller bar 108 thecasting frame 112 on all sides, thus providing a gel material of auniform thickness comparable to the target thickness of the castingframe 112.

Using a casting table allows for the production of aerogel materialswhich are extremely thin compared to standard aerogel materials. Aerogelmaterials of the present invention can have a thickness of less than 10mm, less than 7.5 mm, less than 5 mm, less than 4 mm, less than 3 mm,less than 2 mm, and less than 1 mm. FIG. 3 and FIG. 5 represent apreferred embodiment of the present invention where the aerogel materialhas a thickness of between about 0.07 inches (˜1.75 mm) to about 0.08inches (˜2 mm). FIG. 4 and FIG. 6 represent another preferred embodimentof the present invention where the aerogel material has a thickness ofbetween about 0.03 (˜0.75 mm) inches to about 0.04 inches (˜1 mm). Theseextremely thin aerogel materials are advantageous because they can beincorporated into a broad range of applications which have extremelynarrow space limitations for insulation materials, such as thermalbatteries.

Using a casting table also allows for the production of aerogelmaterials which have a uniform thickness throughout the material.Aerogel materials of the present invention can have a thicknessvariation of less than 15%, less than 10%, less than 8%, less than 6%,less than 5%, less than 4%, less than 3%, and less than 2%. Within thecontext of the present invention, the thickness variation of an aerogelmaterial can be determined by taking at least ten thickness measurementsover the entire area of the aerogel material, calculating the mean andstandard deviation of those thickness measurements, and then dividingthe standard deviation by the mean. FIG. 5 represents a preferredembodiment of the present invention where the aerogel material has athickness of between about 0.07 inches (˜1.75 mm) to about 0.08 inches(˜2 mm), and a thickness variation between about 1.5% and about 8%. FIG.6 represents another preferred embodiment of the present invention wherethe aerogel material has a thickness of between about 0.03 (˜0.75 mm)inches to about 0.04 inches (˜1 mm), and a thickness variation betweenabout 1.5% and about 8%. Thin aerogel materials with uniform thicknessare advantageous because they provide predictable and consistentinsulation characteristics. Thin aerogel materials with uniformthickness have minimal risk of being under-insulating in overly thinregions of the material or over-insulating in overly thick regions ofthe material.

The process of transitioning gel-forming components into a gel materialcan also include an aging step (also referred to as curing) prior toliquid phase extraction. Aging a gel material after it reaches its gelpoint can further strengthen the gel framework by increasing the numberof cross-linkages within the network. The duration of gel aging can beadjusted to control various properties within the resulting aerogelmaterial. This aging procedure can be useful in preventing potentialvolume loss and shrinkage during liquid phase extraction. Aging caninvolve: maintaining the gel (prior to extraction) at a quiescent statefor an extended period; maintaining the gel at elevated temperatures;adding cross-linkage promoting compounds; or any combination thereof.The preferred temperatures for aging are usually between about 10° C.and about 100° C. The aging of a gel material typically continues up tothe liquid phase extraction of the wet-gel material.

The time period for transitioning gel-forming materials into a gelmaterial includes both the duration of the initial gel formation (frominitiation of gelation up to the gel point), as well as the duration ofany subsequent curing and aging of the gel material prior to liquidphase extraction (from the gel point up to the initiation of liquidphase extraction). The total time period for transitioning gel-formingmaterials into a gel material is typically between about 1 minute andseveral days, preferably about 30 hours or less, about 24 hours or less,about 15 hours or less, about 10 hours or less, about 6 hours or less,about 4 hours or less, about 2 hours or less, about 1 hour or less,about 30 minutes or less, or about 15 minutes or less.

The resulting gel material may be washed in a suitable secondary solventto replace the primary reaction solvent present in the wet-gel. Suchsecondary solvents may be linear monohydric alcohols with 1 or morealiphatic carbon atoms, dihydric alcohols with 2 or more carbon atoms,branched alcohols, cyclic alcohols, alicyclic alcohols, aromaticalcohols, polyhydric alcohols, ethers, ketones, cyclic ethers or theirderivative.

Once a gel material has been formed and processed, the liquid phase ofthe gel can then be at least partially extracted from the wet-gel usingmany extraction methods, including innovative processing and extractiontechniques, to form an aerogel material. Liquid phase extraction, amongother factors, plays an important role in engineering thecharacteristics of aerogels, such as porosity and density, as well asrelated properties such as thermal conductivity. Generally, aerogels areobtained when a liquid phase is extracted from a gel in a manner thatcauses low shrinkage to the porous network and framework of the wet gel.

Aerogels are commonly formed by removing the liquid mobile phase fromthe gel material at a temperature and pressure near or above thecritical point of the liquid mobile phase. Once the critical point isreached (near critical) or surpassed (supercritical) (i.e pressure andtemperature of the system is at or higher than the critical pressure andcritical temperature respectively) a new supercritical phase appears inthe fluid that is distinct from the liquid or vapor phase. The solventcan then be removed without introducing a liquid-vapor interface,capillary pressure, or any associated mass transfer limitationstypically associated with liquid-vapor boundaries. Additionally, thesupercritical phase is more miscible with organic solvents in general,thus having the capacity for better extraction. Co-solvents and solventexchanges are also commonly used to optimize the supercritical fluiddrying process.

If evaporation or extraction occurs below the supercritical point,strong capillary forces generated by liquid evaporation can causeshrinkage and pore collapse within the gel material. Maintaining themobile phase near or above the critical pressure and temperature duringthe solvent extraction process reduces the negative effects of suchcapillary forces. In some embodiments of the present invention, the useof near-critical conditions just below the critical point of the solventsystem may allow production of aerogel materials or compositions withsufficiently low shrinkage, thus producing a commercially viableend-product.

Several additional aerogel extraction techniques are known in the art,including a range of different approaches in the use of supercriticalfluids in drying aerogels. For example, Kistler (J. Phys. Chem. (1932)36: 52-64) describes a simple supercritical extraction process where thegel solvent is maintained above its critical pressure and temperature,thereby reducing evaporative capillary forces and maintaining thestructural integrity of the gel network. U.S. Pat. No. 4,610,863describes an extraction process where the gel solvent is exchanged withliquid carbon dioxide and subsequently extracted at conditions wherecarbon dioxide is in a supercritical state. U.S. Pat. No. 6,670,402teaches extracting a liquid phase from a gel via rapid solvent exchangeby injecting supercritical (rather than liquid) carbon dioxide into anextractor that has been pre-heated and pre-pressurized to substantiallysupercritical conditions or above, thereby producing aerogels. U.S. Pat.No. 5,962,539 describes a process for obtaining an aerogel from apolymeric material that is in the form a sol-gel in an organic solvent,by exchanging the organic solvent for a fluid having a criticaltemperature below a temperature of polymer decomposition, andsupercritically extracting the fluid/sol-gel. U.S. Pat. No. 6,315,971discloses a process for producing gel compositions comprising: drying awet gel comprising gel solids and a drying agent to remove the dryingagent under drying conditions sufficient to reduce shrinkage of the gelduring drying. U.S. Pat. No. 5,420,168 describes a process wherebyResorcinol/Formaldehyde aerogels can be manufactured using a simple airdrying procedure. U.S. Pat. No. 5,565,142 describes drying techniques inwhich the gel surface is modified to be stronger and more hydrophobic,such that the gel framework and pores can resist collapse during ambientdrying or subcritical extraction. Other examples of extracting a liquidphase from aerogel materials can be found in U.S. Pat. Nos. 5,275,796and 5,395,805.

One preferred embodiment of extracting a liquid phase from the wet-geluses supercritical conditions of carbon dioxide, including, for example:first substantially exchanging the primary solvent present in the porenetwork of the gel with liquid carbon dioxide; and then heating the wetgel (typically in an autoclave) beyond the critical temperature ofcarbon dioxide (about 31.06° C.) and increasing the pressure of thesystem to a pressure greater than about 1070 psig. The pressure aroundthe gel material is then slightly fluctuated to facilitate removal ofthe supercritical carbon dioxide fluid from the gel. Carbon dioxide canbe recirculated through the extraction system to facilitate thecontinual removal of the primary solvent from the wet gel. Finally, thetemperature and pressure are slowly returned to ambient conditions toproduce a dry aerogel material. Carbon dioxide can also be pre-processedinto a supercritical state prior to being injected into an extractionchamber.

One example of an alternative method of forming an aerogel includes theacidification of basic metal oxide precursors (such as sodium silicate)in water to make a hydrogel. Salt by-products may be removed from thesilicic acid precursor by ion-exchange and/or by washing subsequentlyformed gels with water. Removing the water from the pores of the gel canbe performed via exchange with a polar organic solvent such as ethanol,methanol, or acetone. The liquid phase in the gel is then at leastpartially extracted using innovative processing and extractiontechniques.

Another example of an alternative method of forming aerogels includesreducing the damaging capillary pressure forces at the solvent/poreinterface by chemical modification of the matrix materials in their wetgel state via conversion of surface hydroxyl groups to hydrophobictrimethylsilylethers, thereby allowing for liquid phase extraction fromthe gel materials at temperatures and pressures below the critical pointof the solvent.

The embodiments of the present invention can be practiced using any ofthe processing, drying and treatment techniques discussed herein, aswell as other processing, drying and treatment techniques known to thosein the art for producing aerogels and aerogel materials as definedherein.

Aerogel compositions may be fiber-reinforced with various fiberreinforcement materials to achieve a more flexible, resilient andconformable composite product. The fiber reinforcement materials can beadded to the gels at any point in the gelling process to produce a wet,fibrous gel composition. The wet gel composition may then be dried toproduce a fiber-reinforced aerogel composition. Fiber reinforcementmaterials may be in the form of discrete fibers, woven materials,non-woven materials, battings, webs, mats, and felts. Fiberreinforcements can be made from organic fibrous materials, inorganicfibrous materials, or combinations thereof.

In a preferred embodiment, non-woven fiber reinforcement materials areincorporated into the aerogel composition as continuous sheet ofinterconnected or interlaced fiber reinforcement materials. The processcomprises initially producing a continuous sheet of fiber reinforced gelby casting or impregnating a gel precursor solution into a continuoussheet of interconnected or interlaced fiber reinforcement materials. Theliquid phase may then be at least partially extracted from thefiber-reinforced gel sheets to produce a sheet-like, fiber reinforcedaerogel composition.

Aerogel composition can also include an opacifier to reduce theradiative component of heat transfer. At any point prior to gelformation, opacifying compounds or precursors thereof may be dispersedinto the mixture comprising gel precursors. Examples of opacifyingcompounds include, but are not limited to: Boron Carbide [B₄C],Diatomite, Manganese ferrite, MnO, NiO, SnO, Ag₂O, Bi₂O₃, carbon black,titanium oxide, iron titanium oxide, zirconium silicate, zirconiumoxide, iron (I) oxide, iron (III) oxide, manganese dioxide, irontitanium oxide (ilmenite), chromium oxide, carbides (such as SiC, TiC orWC), or mixtures thereof. Examples of opacifying compound precursorsinclude, but are not limited to: TiOSO₄ or TiOCl₂.

The aerogel materials and compositions of the present invention havebeen shown to be highly effective as insulation materials. However,application of the methods and materials of the present invention arenot intended to be limited to applications related to insulation. Themethods and materials of the present invention can be applied to anysystem or application which would benefit from the unique combination ofproperties or procedures provided by the materials and methods of thepresent invention.

The aerogel materials of the present invention have been shown to bemore effective at maintaining a thermal battery at operationaltemperatures for longer periods of time, as compared to insulationmaterials presently used in thermal batteries. The expected increase inruntime and/or energy capacity has been shown to be more than 50% longerthan the best currently-available insulation.

Within the context of the present invention, the terms “improved batterylife,” “improved battery performance,” or variations thereof refer to anincrease in the duration of time that a thermal battery produces avoltage output at a specified level, with the increase resulting fromthe incorporation of an improved insulation material into the thermalbattery. “Improved battery life” or “improved battery performance” canbe reported as a percentage of the improved battery life relative to theoriginal battery life. For example, a thermal battery having an originalrun time of 300 seconds and an improved run time of 450 seconds has animproved battery life of 150%. “Improved battery life” or “improvedbattery performance” can also be reported as an increase percentage ofthe improved battery life relative to the original battery life. Forexample, a thermal battery having an original run time of 300 secondsand an improved run time of 450 seconds has a battery life increase of50%.

The term “22V run time” refers to the duration of time that a thermalbattery produces a voltage output of 22 V or more after thermalactivation of the battery. The term “16V run time” refers to theduration of time that a thermal battery produces a voltage output of 16Vor more after thermal activation of the battery. The term “1V run time”refers to the duration of time that a thermal battery produces a voltageoutput of 1V or more after thermal activation of the battery. Thus, animproved battery performance for a 22V run time indicates that a thermalbattery is able to produce a voltage output of 22V or more for a longerduration of time after thermal activation, with the increase resultingfrom the incorporation of an improved insulation material into thethermal battery. Voltage output can be measured using an Agilent 34970AData Acquisition Instrument, as well as any other commonly used methodof voltage measurement know in the art. Voltage output measurements areoften temperature dependent. Voltage output measurements of the presentinvention are measured at −65° F. (−54° C.) and 70° F. (21° C.).

An aerogel material of the present invention can provide an improvedthermal battery life when incorporated into a thermal battery. At −54°C., an aerogel material of the present invention can provide an improvedthermal battery life of: i) up to about 300% improved batteryperformance for a 1V run time; up to about 250% improved batteryimproved battery performance for a 16V run time; and up to about 200%improved battery performance for a 22 V run time. At 21° C., an aerogelmaterial of the present invention can provide an improved thermalbattery life of: i) up to about 215% improved battery performance for a1V run time; up to about 200% improved battery improved batteryperformance for a 16V run time; and up to about 175% improved batteryperformance for a 22V run time.

The following examples provide various embodiments and properties of thepresent invention.

Example 1—Casting Table

FIG. 2 illustrates a casting table 100 which was used for the productionof thin sheets of Fiber-Reinforced Aerogel Materials. A 4 ft×6 ft sheetof PETG (polyethylene terephthalate glycol-modified) having a thicknessof 0.078 inches (˜2 mm) was placed onto a Teflon-covered 4 ft×6 fttable. A 3 ft×5 ft rectangle of PETG material was cut and removed fromthe interior of the PETG sheet. The remaining PETG material providedthickness control during the subsequent casting of the aerogel material.The thickness of the PETG material was chosen to provide a final castthickness of 0.070 inches (˜1.75 mm) for the aerogel insulationmaterial.

The resulting casting table 100 comprised a 3 ft×5 ft casting area 102,enclosed by a rectangular PETG casting frame which was 0.078 inchesthick (˜2 mm), and which had a perimeter of 4 ft×6 ft on the exterioredges 106, a perimeter of 3 ft×5 ft on the interior edges 104, and auniform 1 ft width from the outer edges 106 to the inner edges 104. Aroller bar 108 was used to spread a gelling solution throughout afibrous batting during preparation of the aerogel insulation materials.

Example 2—Preparation of Fiber-Reinforced Aerogel Materials

FIGS. 1 a-1 h illustrate a method for producing thin aerogel materialsof a uniform thickness. A sol-gel solution with a target density of 0.06g/cc was prepared by hydrolyzing tetraethyl orthosilicate (TEOS) andmethyltriethoxy silane (MTES) in the presence of acid. SiC F1200 Black(Carborex© F1200, Washington Mills) was added to the sol-gel solution.

A lofty fiber batting (Quartzel©, Saint-Gobain Quartz) was placed intothe casting area of the casting table of Example 1 (FIG. 1 a ). Ammoniawas added to the sol-gel solution to initiate gelation. The sol-gelsolution was then applied over a large portion of the batting material(FIGS. 1 c and 1 d ). A nonporous Teflon sheet was placed over thecasting table to minimize loss of ammonia during the casting process(FIG. 1 e ).

While the sol-gel solution was still in a substantially fluid state, thesolution was spread throughout the batting using a roller. A roller barwas placed on one end of the casting frame (FIG. 1 b ). The roller barwas then rolled along the length of the casting frame while maintainingcontact with the top surface of the casting frame (FIG. 1 f ). Theweight and motion of the rolling bar functioned to evenly distribute thegelling solution throughout the batting material. Maintaining contactbetween the roller bar and the casting frame assured uniform thicknessof the gel throughout the batting. The rolling process was continuedthrough a gelation time of 2.5 minutes.

After gelation was complete (FIG. 1 g ), the composite sheets were agedfor 16 hours in an ethanol solution with 8.5% H2O (v/v), 1.1 g/100 ml ofammonia, and 0.1M TMS at 68° C. The wet-gel composites were thensubjected to supercritical CO2 drying to produce a thin sheet of dryfiber-reinforced aerogel material.

The sheets of dry fiber-reinforced aerogel material were thenheat-treated at 183° C. for 40 minutes, followed by calcination in airat 600° C. The heating profile for calcination at 600° C. involved threesteps: 1) ramp to 600° C. with a ramp rate of 20° C./min; 2) dwell at600° C. for 6 hours; and 3) cool down to room temperature naturally.

Example 3—Thickness Testing

A sheet of aerogel material from example 2 was cut into 8 in×8 incoupons for testing (FIG. 1 h ). Sixteen thickness measurements weremade on each of eighteen different coupons (for a total of 288measurements) using a hand-held drop-gauge. These measurements were usedto determine the overall thickness variation in a composite sheet, aswell as product yield (based on thickness).

FIG. 5 shows the average thickness measurements for all 18 coupons,presented along with the respective variation percentages. All couponsexhibited thickness variation below 7%. At 100% yield, the overallaverage thickness was 0.0759″ with 4.6% variation. Coupons prepared bythis method demonstrated good particle dispersion and low thicknessvariation.

Example 4—Thermal Conductivity Testing

Coupons of aerogel material were prepared according to examples 1-3above. The coupons were tested for thermal conductivity on a Guarded HotPlate (GHP) according to ASTM C177 measuring standards, at temperaturesup to 650° C. The results of the thermal conductivity measurements areshown in FIGS. 7-8 .

Example 5—Flexural Testing

Coupons of aerogel material were prepared according to examples 1-3above. The coupons were tested for flexure properties under ASTM C1101testing standards. It was found that during flexure testing, the aerogelmaterial did not rupture or break. The aerogel sheet materials were thusclassified as flexible according to ASTM C1101 classification standards.

It was also found that the aerogel materials returned to original formwhen released from flexural testing. The aerogel sheet materials werethus classified as resilient flexible according to ASTM C1101classification standards.

Example 6—Battery Performance Testing

Fifteen batteries were manufactured using G3190B2 thermal batteries fromEnersys®, and test fired at −65° F. (−54° C.) and 70° F. (21° C.). Thebatteries can be identified according to the following insulationconfigurations: i) 5 Batteries built as control units using standardFiberfrax® insulation for both the outer and inner wraps(Fiberfrax-Fiberfrax); 5 Batteries made using aerogel wrap insulationfor both the outer and inner wraps (Aerogel-Aerogel); 5 Batteries madeusing Fiberfrax® insulation for the inner wrap and aerogel wrapinsulation for the outer wrap (Fiberfrax-Aerogel).

Prior to testing the batteries were conditioned to their respectiveenvironments: Room temperature: 66.2° F. (19° C.); and Cold temperature:−65° F. (−54° C.).

Voltage data was gathered with a calibrated Agilent 34970A DataAcquisition Instrument and the raw data was gathered at a rate of eachL>second on a HP laptop computer. Voltage and temperature profiles weregathered versus time for all 15 test fired batteries. The results of thebattery performance testing are shown in FIGS. 9-10 .

Both the Aerogel-Aerogel and the Fiberfrax-Aerogel insulationconfigurations increased the amount of time that heat was maintained inthe core of the battery's electrochemical cell, thus increasing thelifetime of the battery. Test firings at −65° F. (−54° C.) showed anaverage 103% increase in lifetime for the Aerogel-Aerogel wrappedbattery (603 seconds) over the Fiberfrax-Fiberfrax control battery (297seconds) tested at the same temperature.

What is claimed:
 1. A reinforced aerogel composition comprising: anaerogel framework and a reinforcement material, the reinforced aerogelcomposition having an average thickness of 10 mm or less and a thicknessvariation of less than 15%.
 2. The reinforced aerogel composition ofclaim 1, wherein the reinforcement material comprises one or more of anopen-cell foam reinforcement material, a polymeric reinforcementmaterial, and a fiber reinforcement material.
 3. The reinforced aerogelcomposition of claim 2, wherein the fiber reinforcement materialcomprises discrete fibers, a woven material, a non-woven material, abatting, a web, a mat, a felt, or a combination thereof.
 4. Thereinforced aerogel composition of claim 2, wherein the fiberreinforcement material comprises glass-based fibers.
 5. The reinforcedaerogel composition of claim 2, wherein the fiber reinforcement materialcomprises silica-based fibers.
 6. The reinforced aerogel composition ofclaim 2, wherein the fiber reinforcement material comprises ceramicfibers.
 7. The reinforced aerogel composition of claim 1, wherein theaverage thickness is about 5 mm and the thickness variation is less than10%.
 8. The reinforced aerogel composition of claim 1, wherein theaverage thickness is about 2 mm and the thickness variation is less than6%.
 9. The reinforced aerogel composition of claim 1, wherein thereinforced aerogel composition has a thermal conductivity of about 25mW/mK or less.
 10. The reinforced aerogel composition of claim 5,wherein the reinforced aerogel composition has a thermal conductivity ina range of about 12 mW/mK and about 20 mW/mK.
 11. The reinforced aerogelcomposition of claim 1, wherein the reinforced aerogel composition has athermal conductivity of about 50 mW/mK or less.
 12. The reinforcedaerogel composition of claim 1, wherein the reinforced aerogelcomposition has a thermal conductivity of between about 12 mW/mK andabout 50 mW/mK.
 13. The reinforced aerogel composition of claim 1,wherein the reinforced aerogel composition includes a silica-basedframework.
 14. The reinforced aerogel composition of claim 1, whereinthe reinforced aerogel composition has a density in a range of about0.60 g/cc and about 0.30 g/cc.
 15. The reinforced aerogel composition ofclaim 1, wherein the average thickness is 5 mm or less.
 16. Thereinforced aerogel composition of claim 1, wherein the average thicknessis 3 mm or less.
 17. The reinforced aerogel composition of claim 1,wherein the average thickness is 1 mm or less.
 18. The reinforcedaerogel composition of claim 1, wherein the reinforced aerogelcomposition is a flexible aerogel blanket composition.
 19. Thereinforced aerogel composition of claim 1, wherein the reinforcedaerogel composition has a resilience of more than 50%.
 20. Thereinforced aerogel composition of claim 1, wherein the reinforcedaerogel composition has a resilience of more than 75%.
 21. Thereinforced aerogel composition of claim 1, wherein the reinforcedaerogel composition has a resilience of more than 90%.
 22. Thereinforced aerogel composition of claim 1, wherein the reinforcedaerogel composition has a resilience of more than 95%.
 23. A batterycomprising the aerogel reinforced composition of claim
 1. 24. A methodof improving performance of a battery comprising incorporating thereinforced aerogel composition of claim 1 into the battery.
 25. Areinforced aerogel composition comprising: an aerogel framework and areinforcement material, the reinforced aerogel composition having anaverage thickness of 5 mm or less and a thickness variation of less than15%.
 26. The reinforced aerogel composition of claim 25, having anaverage thickness of 5 mm and a thickness variation of less than 10%.27. The reinforced aerogel composition of claim 25, having an averagethickness of 5 mm and a thickness variation of less than 5%.
 28. Thereinforced aerogel composition of claim 25, wherein the reinforcedaerogel composition is a flexible aerogel blanket composition.
 29. Thereinforced aerogel composition of claim 25, wherein the reinforcedaerogel composition has a thermal conductivity of about 25 mW/mK orless.
 30. The reinforced aerogel composition of claim 25, wherein thereinforced aerogel composition has a thermal conductivity of betweenabout 12 mW/mK and about 20 mW/mK.
 31. The reinforced aerogelcomposition of claim 25, wherein the aerogel framework comprises anorganic aerogel.